diff --git a/crates/rfc5321/src/client.rs b/crates/rfc5321/src/client.rs
index 25953a00..8c902c1b 100644
--- a/crates/rfc5321/src/client.rs
+++ b/crates/rfc5321/src/client.rs
@@ -1,5 +1,8 @@
 use crate::client_types::*;
-use crate::{AsyncReadAndWrite, BoxedAsyncReadAndWrite, Command, Domain, ForwardPath, ReversePath};
+use crate::{
+    AsyncReadAndWrite, BoxedAsyncReadAndWrite, Command, Domain, EsmtpParameter, ForwardPath,
+    ReversePath,
+};
 use hickory_proto::rr::rdata::tlsa::{CertUsage, Matching, Selector};
 use hickory_proto::rr::rdata::TLSA;
 use memchr::memmem::Finder;
@@ -642,15 +645,47 @@ impl SmtpClient {
         recipient: RECIP,
         data: B,
     ) -> Result<Response, ClientError> {
+        let sender = sender.into();
+        let recipient = recipient.into();
+
+        let data: &[u8] = data.as_ref();
+        let stuffed;
+
+        let data = match apply_dot_stuffing(data) {
+            Some(d) => {
+                stuffed = d;
+                &stuffed
+            }
+            None => data,
+        };
+
+        let data_is_8bit = data.iter().any(|&b| b >= 0x80);
+        let envelope_is_8bit = !sender.is_ascii() || !recipient.is_ascii();
+
+        let mut mail_from_params = vec![];
+        if data_is_8bit && self.capabilities.contains_key("8BITMIME") {
+            mail_from_params.push(EsmtpParameter {
+                name: "BODY".to_string(),
+                value: Some("8BITMIME".to_string()),
+            });
+        }
+
+        if envelope_is_8bit && self.capabilities.contains_key("SMTPUTF8") {
+            mail_from_params.push(EsmtpParameter {
+                name: "SMTPUTF8".to_string(),
+                value: None,
+            });
+        }
+
         let mut responses = self
             .pipeline_commands(vec![
                 Command::Rset,
                 Command::MailFrom {
-                    address: sender.into(),
-                    parameters: vec![],
+                    address: sender,
+                    parameters: mail_from_params,
                 },
                 Command::RcptTo {
-                    address: recipient.into(),
+                    address: recipient,
                     parameters: vec![],
                 },
                 Command::Data,
@@ -704,16 +739,6 @@ impl SmtpClient {
             return Err(ClientError::Rejected(data_resp));
         }
 
-        let data: &[u8] = data.as_ref();
-        let stuffed;
-
-        let data = match apply_dot_stuffing(data) {
-            Some(d) => {
-                stuffed = d;
-                &stuffed
-            }
-            None => data,
-        };
         let needs_newline = data.last().map(|&b| b != b'\n').unwrap_or(true);
 
         tracing::trace!("message data is {} bytes", data.len());
diff --git a/crates/rfc5321/src/parser.rs b/crates/rfc5321/src/parser.rs
index b2e1a01c..ca52a1b5 100644
--- a/crates/rfc5321/src/parser.rs
+++ b/crates/rfc5321/src/parser.rs
@@ -204,6 +204,15 @@ pub enum ReversePath {
     NullSender,
 }
 
+impl ReversePath {
+    pub fn is_ascii(&self) -> bool {
+        match self {
+            Self::Path(path) => path.is_ascii(),
+            Self::NullSender => true,
+        }
+    }
+}
+
 impl TryFrom<&str> for ReversePath {
     type Error = String;
     fn try_from(s: &str) -> Result<Self, Self::Error> {
@@ -241,6 +250,15 @@ pub enum ForwardPath {
     Postmaster,
 }
 
+impl ForwardPath {
+    pub fn is_ascii(&self) -> bool {
+        match self {
+            Self::Path(p) => p.is_ascii(),
+            Self::Postmaster => true,
+        }
+    }
+}
+
 impl TryFrom<&str> for ForwardPath {
     type Error = String;
     fn try_from(s: &str) -> Result<Self, Self::Error> {
@@ -280,6 +298,14 @@ pub struct MailPath {
     pub mailbox: Mailbox,
 }
 
+impl MailPath {
+    pub fn is_ascii(&self) -> bool {
+        // Note: ignoring at_domain_list here per the to_string()
+        // implementation
+        self.mailbox.is_ascii()
+    }
+}
+
 impl ToString for MailPath {
     fn to_string(&self) -> String {
         // Note: RFC5321 says about at_domain_list:
@@ -298,6 +324,18 @@ pub struct Mailbox {
     pub domain: Domain,
 }
 
+impl Mailbox {
+    pub fn is_ascii(&self) -> bool {
+        if !self.local_part.is_ascii() {
+            return false;
+        }
+        match &self.domain {
+            Domain::V4(s) | Domain::V6(s) | Domain::Name(s) => s.is_ascii(),
+            Domain::Tagged { tag, literal } => tag.is_ascii() && literal.is_ascii(),
+        }
+    }
+}
+
 impl ToString for Mailbox {
     fn to_string(&self) -> String {
         let domain = self.domain.to_string();